Measurement and/or control of humidity and temperature of a gaseous fluid in a textile treating chamber, whether it is for drying or heat setting or other purposes, plays a vital role in assuring quality, maximum efficiency and productivity of the system. In the past, humidity measurement devices using various types of sensors failed to meet the tough requirements of a textile processing environment wherein the gaseous fluids contained lint, fumes, condensable oils, tints and resins, or the like, as these contaminants fouled the wick of the wet bulb sensing element after a period of use. In order to obviate the difficulty in utilizing simple humidity measuring devices which used a wet bulb sensor with a wick, highly-sophisticated systems were made available for use in the textile field, but these systems had the drawback that they required skilled technicians for operation and maintenance. Additionally, these highly-sophisticated systems had a high initial cost of installation.